Although it is well documented that an estimated 85 percent of lung cancer may be attributable to cigarette smoking, only 10-20 percent of smokers develop lung cancer during their lifetime indicating clearly that there is more to its initiation than the simple inhalation of cigarette smoke. This is suggestive of numerous other environmental and genetic factors that may be implicated in the pathogenesis of the disease. Although the molecular epidemiology has made progress in documenting carcinogenic exposures and host susceptibility factors for lung cancer, unfortunately, many of these exposure risk factors are only identified individually. The state of knowledge has advanced to the point that these risk factors should be investigated in conjunction with multiple host susceptibility factors so that gene-environmental interactions can be assessed. We propose to take advantage of the recent advances in molecular techniques to analyze human samples for genetic polymorphisms affecting nutritional status, global and gene specific DNA methylation so that these factors can be studied along with known risk factors for lung cancer, including inherited mutations in tumor suppressor genes and oncogenes. This may shed light on the sources of variability that may affect inherited or acquired susceptibility to lung cancer. The hypothesis to be tested in this proposal is that there are important genetic and epigenetic differences between smokers who develop lung cancer compared to those who do not. We will focus our study on a genetic polymorphism (methylene tetrahydrofolate reductase [MTHFR]) that might affect the status, most likely, of a locally deficient concentration of a specific vitamin (folate) in the lung and associated changes in DNA critical for the development of cancer. To test this hypothesis, the frequency of MTHFR polymorphism, global and gene specific methylation and the expression of several intermediate end point biomarkers will be compared between 60 smokers who developed squamous cell lung cancer (SCC) and 60 smokers who did not. Interactions among and between these variables will also be investigated. The results generated by this study will be used to conduct a well-designed molecular epidemiological study of lung cancer.